Numerous methods have been proposed in the prior art for distributing information using an optical fiber, preferred methods including star, ring and bus architectural networks. Generally speaking, star and ring networks utilize point-to-point connections, whereas bus networks are capable of utilizing non-point-to-point connections whereby an optical signal is only partially interrupted by any one connection.
For example, Polcyzynski, U.S. Pat. No. 4,089,584 discloses a bus network which utilizes an optical fiber having a rectangular core and cladding, and connection or tapping of the fiber is accomplished by removing the cladding and disposing a prism or grading against an exposed rectangular core. Such networks are disadvantageous, since the fiber and taps usable therewith are relatively complex in design and hence unduly expensive, and optical network performance is rather poor in view of relatively low tapping efficiencies that result using such methods.
Miller, United Kingdom Patent document No. 2,126,749B and an article by Dakin et al. entitled "Experimental Studies into the Non-Invasive Collection and Distribution of Data on a Fiber-Optic Monomode Bus" propose designing a read optical fiber bus using taps whereby light is withdrawn through a side of the optical fiber by passing the light through a coating of the fiber. Miller collects the light from the bus fiber by disposing a photodetector at an end of a curved and grooved light pipe disposed around the bus fiber, and Dakin et al. collects the light by tightly pressing a polymeric fiber with part of its cladding removed against a curved portion of the bus fiber. Such techniques are also disadvantageous in that again the taps are complicated in design, require special technician/craft skills and are craft sensitive to install in the field, and are not sufficiently efficient when tight flux budgets are mandated by network design.
Goell et al., U.S. Pat. No. 3,982,123 at FIGS. 5A and 5B disclose an optical fiber read tap whereby an exposed glass cladding of a bent optical fiber portion is glued to a top of a photodetector. Such taps are disadvantageous since a strength of the fiber is disadvantageously affected by removal of its outer protective buffer, and rather small coupling light efficiencies are obtained by simply using epoxy to secure a bent optical fiber onto a top surface of a photodetector. In addition, the optical fiber is not releaseable from the tap.
Cross, U.S. Pat. No. 4,270,839 discloses a tap for an optical fiber whereby the fiber is bent in air, and downstream from the bent portion of the optical fiber a straight section of the optical fiber is glued within a straight light pipe which thereafter is curved and has a light detector at a remote end thereof. Again, such taps are disadvantageous, since they have been found to yield relatively low light coupling efficiencies, and the optical fiber is not releaseable from the pipe once glued thereonto.
Campbell et al., U.S. Pat. No. 4,728,169; Campbell et al., U.S. patent application Ser. No. 754,035, filed on July 11, 1985; and Campbell et al., U.S. patent application Ser. No. 614,884, filed on May 25, 1984, all of which are assigned to the assignee of the present invention, the disclosures of which are all incorporated herein by reference, disclose several advantageous kinds of taps for injecting light into, or withdrawing light from, optical fibers. However, there continues to be a need for yet more efficient taps which are also mechanically simple in structure and reliably usable in the field without special craft skills or extensive training.